Functional Analysis of O-GlcNAc Modifications using Synthetic Protein Chemistry O-GlcNAc modification (O-GlcNAcylation) is a dynamic protein-modification that is absolutely required for embryonic development in mammals, and is misregulated in diseases, including diabetes, neurodegeneration and cancer. Although approximately 1000 potential proteins are modified by O-GlcNAc, the effects of the vast majority of these modifications on protein function are completely unknown. This critical lack of knowledge exists in-part because traditional methods are deficient for the study of site-specific O-GlcNAcylation events. The long-term goal of our research program is to understand the consequences of O-GlcNAcylation on proteins that are key to human disease. The objectives of this application are to develop protein engineering strategies that uniquely enable the generation of proteins with site-specific O-GlcNAc modifications and to apply these methods to understand the effects of O-GlcNAcylation on the protein a-synuclein, the aggregation-prone protein in Parkinson's disease. Our preliminary studies demonstrate that homogeneously O-GlcNAcylated proteins can be prepared using synthetic chemistry. Furthermore, we have used synthetic protein chemistry to demonstrate that O-GlcNAcylation blocks a-synuclein aggregation. Guided by these preliminary studies, we will: 1) continue to develop general synthetic-strategies for the preparation of O-GlcNAcylated proteins, 2) investigate the molecular mechanism by which O-GlcNAcylation blocks a-synuclein aggregation and 3) determine the effects of O-GlcNAcylation on the cellular toxicity of a-synuclein. These studies are significant, as the effects of O-GlcNAcylation are almost completely unknown. Additionally, blocking a-synuclein aggregation is a key potential therapeutic strategy in Parkinson's disease. Our approach is also innovative as it enables the effects of O-GlcNAcylation to be directly tested in a site-specific fashion and can be applied to other critical proteins in the future.